Molecular sieves are a commercially important class of crystalline materials. They have distinct crystal structures with ordered pore structures which are demonstrated by distinct X-ray diffraction patterns. The crystal structure defines cavities and pores which are characteristic of the different species.
Molecular sieves identified by the International Zeolite Associate (IZA) as having the structure code CHA are known. For example, the molecular sieve known as SSZ-13 is a known crystalline CHA material. It is disclosed in U.S. Pat. No. 4,544,538, issued Oct. 1, 1985 to Zones. In that patent, the SSZ-13 molecular sieve is prepared in the presence of a N-alkyl-3-quinuclidinol cation, a N,N,N-trialkyl-1-adamantammonium cation and/or, and N,N,N-trialkyl-2-exoaminonorbornane cation as the structure-directing agent (SDA).
U.S. Publication No. 2007-0286798 to Cao et al., published Dec. 13, 2007, discloses the preparation of CHA-type molecular sieves using various SDAs, including a N,N,N-trimethyl-2-adamantammonium cation.
However, SDAs useful for making CHA materials are complex and typically not available in quantities necessary to produce CHA materials on a commercial scale. In addition, there is a continuous need to reduce the concentration of known CHA SDAs in the reaction mixture to an absolute minimum, or replace them entirely with SDAs that are cheaper, less complex and/or reduce the time necessary to form product.
It has now been found that CHA-type molecular sieves can be prepared using an alkali metal silicate and at least one of the novel structure directing agents described herein below.